As a natural phospholipid compound, there has been known platelet-activating factor (PAF) representable by the formula: ##STR2## [wherein R.sup.1 stands for hexadecyl or octadecyl]. Synthetic phospholipid compounds resembling the compound (II) are known to have PAF-like actions such as platelet-activating action, neutrophil activating activity, tissue-impairing action, vascular-permeability increasing action, hypotensive action or the like, though some differences in the strength of these actions of the respective compounds due to the structural differences are observed. On the other hand, as a derivative of natural phosphatidyl choline, there has been known the synthetic phospholipid compound representable by the formula: ##STR3## [e.g. Japanese Unexamined Patent Publication No. 52-134027 (1977)]. This compound (III) has, unlike natural phospholipid compounds, an anti-tumor activity as well as platelet aggregation activity [D. J. Hanahan et al., Biochem.Biophys. Res. Commun. 99, 183 (1981)].
This sort of action against platelets reises concern about serious circulatory disturbances such as cerebal thrombosis and angina pectoris.
The compound (III) has been recognized to show a hypotensive action and also an action of local irritation and/or damage. These actions are side actions which prevent the compound (III) from being used it as a medicine. In some of the references concerned [e.g. Thrombosis Research 30, 143 (1983)], there is disclosed a phospholipid compound of the formula: ##STR4## but this compound also shows platelet aggregation action.
As further examples of phospholipid compounds structurally resembling those of the formula (I), there are mentioned compounds which are included in the claims of Japanese Unexamined Patent Publication No. 58-192825 (1983). Among them, however, the compound shown by the formula ##STR5## having a carbonyl group introduced at the 2-position, also shows platelet aggregation action, and thus the use of the compound as a medicine is restricted to some extent.
As described above, synthetic phospholipid compounds having a relatively small substituent at 2-position show PAF-like actions, and the use of them as medicines leaves problems to be solved because of the afore-mentioned reasons.
While a compound of the formula ##STR6## is disclosed in Japanese Unexamined Patent Publication No. 58-35194 (1983), the antitumor effect of this compound (VI) can hardly be considered sufficient.
Synthetic phospholipids, especially those which have relatively small substituents at the 2-position, in general, show actions as mentioned above, such as platelet aggregation action, hypotensive action, etc. These actions, when synthetic phospholipids are used as anti-tumor agents, are undesirable side-actions. Furthermore, the effective dose as antitumor agent is quite near the amount of causing those side actions. Therefore, these synthetic phospholipid compounds are extremely difficult to be used as anti-tumor agents as they are. For separation of the antitumor effect from the PAF activities such as platelet aggregation, hypotensive action, etc., the present inventors made extensive studies and researches. As the result, the present inventors found out that the phospholipid compounds representable by the formula (I) showed substantially no action due to the PAF action, more specifically, disappearance of platelet aggregation and remarkable weakening of hypotensive actions, while they show remarkable anti-tumor actions.
Thus, the present inventors found that the difference between the dose for exerting anti-tumor effect and the amount of causing the side-actions was remarkably enlarged, and also that the compound (I) of this invention had an effect of inhibition against proliferation of myeologenous leukemia HL-60 as well as differentiation inducing activity, to lead to the completion of the present invention.